Insects, nematodes, and related arthropods annually destroy an estimated 15% of agricultural crops in the United States and even more than that in developing countries. In addition, competition with weeds and parasitic and saprophytic plants account for even more potential yield losses.
Some of this damage occurs in the soil when plant pathogens, insects and other such soil borne pests attack the seed after planting. In the production of corn, for example, much of the rest of the damage is caused by rootworms—insect pests that feed upon or otherwise damage the plant roots; and by cutworms, European corn borers, and other pests that feed upon or damage the above ground parts of the plant. General descriptions of the type and mechanisms of attack of pests on agricultural crops are provided by, for example, Metcalf (1962) in Destructive and Useful Insects: Their Habits and Control, Fourth Edition. (Earlier editions by C. L. Metcalf and W. P. Flint) McGraw-Hill Book Company; New York, San Francisco, Toronto, London; and Agrios, (1988) in Plant Pathology, 3.sup.rd Ed., Academic Press.
Lepidopteran insects cause considerable damage to maize crops throughout North America and the world. One of the leading pests is Ostrinia nubilalis, commonly called the European Corn Borer (ECB). Genes encoding the crystal proteins Cry1A(b) and Cry1A(c) from Bt have been introduced into maize as a means of ECB control. The Cry1 group includes, but is not limited to, Cry1A(a), Cry1A(b) and Cry1A(c). See Hofte et al (1989) Microbiol Rev 53: 242-255. These transgenic maize hybrids have been effective in control of ECB (U.S. Pat. Nos. 6,180,744, 5,689,052 and U.S. publication 2002/013227). Recently, Cry1F expressing maize hybrids have also been developed for control of ECB (Chambers, et al. (1991). J. Bact. 173:3966-3976 and Herman, et al. (2002). J. Agric. Food Chem. 50:7076-7078, U.S. Pat. Nos. 5,691,308, 5,188,960 and WO 99/24581). However, developed resistance to Bt toxins presents a challenge in pest control. See McGaughey et al. (1998) Nature Biotechnology 16: 144-146; Estruch et al. (1997) Nature Biotechnology 15:137-141; Roush et al. (1997) Nature Biotechnology 15 816-817; and Hofte et al (1989) supra.
The primary site of action of Cry1 toxins is in the brush border membranes of the midgut epithelia of susceptible insect larvae such as Lepidopteran insects. Cry1A toxin binding polypeptides have been characterized from a variety of Lepidopteran species. A Cry1A(c) binding polypeptide with homology to an aminopeptidase N has been reported from Manduca sexta, Lymantria dispar, Helicoverpa zea and Heliothis virescens. See Knight et al. (1994) Mol Micro 11: 429-436; Lee et al. (1996) Appl Environ Micro 63: 2845-2849; Gill et al. (1995) J Biol. Chem 270: 27277-27282; and Garczynski et al. (1991) Appl Environ Microbiol 10: 2816-2820.
Another Bt toxin binding polypeptide (BTR1) cloned from M. sexta has homology to the cadherin polypeptide superfamily and binds Cry1A(a), Cry1A(b) and Cry1A(c). See Vadlamudi et al. (1995) J Biol Chem 270(10):5490-4, Keeton et al. (1998) Appl Environ Microbiol 64(6):2158-2165; Keeton et al. (1997) Appl Environ Microbiol 63(9):3419-3425 and U.S. Pat. No. 5,693,491.
A subsequently cloned homologue to BTR1 demonstrated binding to Cry1A(a) from Bombyx mori as described in Thara et al. (1998) Comparative Biochemistry and Physiology, Part B 120:197-204 and Nagamatsu et al. (1998) Biosci. Biotechnol. Biochem. 62(4):727-734.
Other serious insect pests of corn in the Midwestern United States are the larval forms of three species of Diabrotica beetles. These include the Western corn rootworm, Diabrotica virgifera virgifera LeConte, the Northern corn rootworm, Diabrotica barberi Smith and Diabrotica barberi Lawrence, and the Southern corn rootworm, Diabrotica undecimpunctata howardi Barber.
Corn rootworms (CRW) overwinter in the egg state in fields where corn was grown the previous season. The eggs hatch from late May through June. If a corn crop is not followed by another corn crop in the subsequent year, the larvae will die. Accordingly, the impact of corn rootworm is felt most directly in areas where corn is systematically followed by corn, as is typical in many areas of the Midwestern United States.
There is evidence of the emergence of a new race of corn rootworm which ovipositions its eggs for overwintering onto adjacent soybean plants. The most common practice in the mid-western United States has been for fields to be rotated annually with corn, followed the next year with soybeans, in order to manage the development of an epidemic of corn rootworm pressure on fields of corn. While this strategy overall has been successful in reducing the corn rootworm feeding pressure on corn in many areas, the evolutionary emergence of this new race of corn rootworm creates a problem which was not anticipated and which could not have been easily foreseen. This new race, which preferentially deposits its eggs onto soybean fields, provides an unintended feeding pressure on the next year's intended corn crop in the field in which soybeans were grown the previous year, and the subsequent requirement for insecticidal control measures which adds unintended cost to the farmer in the form of additional labor for spraying and additional costs of goods, further reducing the return to the farmer on his/her investment in the crop and harvest.
The western corn rootworm (WCRW), D. virgifera virgifera, is a widely distributed pest of corn in North America, and in many instances, chemical insecticides are indiscriminately used to keep the numbers of rootworms below economically damaging levels. In order to assist in the reduction of chemical insecticides used in treatments to control the rootworm population in crop fields, transgenic lines of corn have been developed which produce one of a number of amino acid sequence variants of an insecticidal protein produced naturally in the bacterium Bacillus thuringiensis. One such protein, generally referred to as Cry3Bb, has recently been modified by English et al., in U.S. Pat. No. 6,023,013 and related patents and applications, to contain one or more amino acid sequence variations which, when tested in insect bioassay against the corn rootworm, demonstrates from about seven (7) to about ten (10) fold increase in insecticidal activity when compared to the wild type amino acid sequence. Another Bt toxin that has been found to be effective in transgenic plants for the control of WCRW is Cry34/35 (U.S. Pat. Nos. 6,548,291, 6,083,499, 6,128,180, 6,624,145 and 6,677,148).
As indicated above, one concern is that resistant ECB and WCRW will emerge. One strategy for combating the development of resistance is to select a recombinant corn event which expresses high levels of the insecticidal protein such that one or a few bites of a transgenic corn plant would cause at least total cessation of feeding and subsequent death of the pest.
Another strategy would be to combine a second ECB or WCRW specific insecticidal protein in the form of a recombinant event in the same plant or in an adjacent plant, for example, another Cry protein or alternatively another insecticidal protein such as a recombinant acyl lipid hydrolase or insecticidal variant thereof (WO 01/49834). Preferably the second toxin or toxin complex would have a different mode of action than the first toxin, and preferably, if receptors were involved in the toxicity of the insect to the recombinant protein, the receptors for each of the two or more insecticidal proteins in the same plant or an adjacent plant would be different so that if a change of function of a receptor or a loss of function of a receptor developed as the cause of resistance to the particular insecticidal protein, then it should not and likely would not affect the insecticidal activity of the remaining toxin which would be shown to bind to a receptor different from the receptor causing the loss of function of one of the two insecticidal proteins cloned into a plant. Accordingly, the first one or more transgenes and the second one or more transgenes are each, respectively insecticidal to the same target insect and bind without competition to different binding sites in the gut membranes of the target insect.
Still another strategy would combine a chemical pesticide with a pesticidal protein expressed in a transgenic plant. This could conceivably take the form of a chemical seed treatment of a recombinant seed which would allow for the dispersal into a zone around the root of a pesticidally controlling amount of a chemical pesticide which would protect root tissues from target pest infestation so long as the chemical persisted or the root tissue remained within the zone of pesticide dispersed into the soil.
Because of concern about the impact of chemical pesticides on public health and the health of the environment, significant efforts have been made to find ways to reduce the amount of chemical pesticides that are used. Recently, much of this effort has focused on the development of transgenic crops that are engineered to express insect toxicants derived from microorganisms. For example, U.S. Pat. No. 5,877,012 to Estruch et al. discloses the cloning and expression of proteins from such organisms as Bacillus, Pseudomonas, Clavibacter and Rhizobium into plants to obtain transgenic plants with resistance to such pests as black cutworms, armyworms, several borers and other insect pests. Publication WO/EP97/07089 by Privalle et al. teaches the transformation of monocotyledons, such as corn, with a recombinant DNA sequence encoding peroxidase for the protection of the plant from feeding by corn borers, earworms and cutworms. Jansens et al. (1997) Crop Sci., 37(5): 1616-1624, reported the production of transgenic corn containing a gene encoding a crystalline protein from Bacillus thuringiensis (Bt) that controlled both generations of ECB. U.S. Pat. Nos. 5,625,136 and 5,859,336 to Koziel et al. reported that the transformation of corn with a gene from B. thuringiensis that encoded for delta-endotoxins provided the transgenic corn with improved resistance to ECB. A comprehensive report of field trials of transgenic corn that expresses an insecticidal protein from B. thuringiensis has been provided by Armstrong et al., in Crop Science, 35(2):550-557 (1995).
Another alternative to the conventional forms of pesticide application is the treatment of plant seeds with pesticides. The use of fungicides or nematicides to protect seeds, and young roots and shoots from attack after planting and sprouting, and the use of low levels of insecticides for the protection of, for example, corn seed from wireworm, has been used for some time. Seed treatment with pesticides has the advantage of providing for the protection of the seeds, while minimizing the amount of pesticide required and limiting the amount of contact with the pesticide and the number of different field applications necessary to attain control of the pests in the field.
Other examples of the control of pests by applying insecticides directly to plant seed are provided in, for example, U.S. Pat. No. 5,696,144, which discloses that ECB caused less feeding damage to corn plants grown from seed treated with a 1-arylpyrazole compound at a rate of 500 g per quintal of seed than control plants grown from untreated seed. In addition, U.S. Pat. No. 5,876,739 to Turnblad et al. (and its parent, U.S. Pat. No. 5,849,320) disclose a method for controlling soil-borne insects which involves treating seeds with a coating containing one or more polymeric binders and an insecticide. This reference provides a list of insecticides that it identifies as candidates for use in this coating and also names a number of potential target insects.
Although recent developments in genetic engineering of plants have improved the ability to protect plants from pests without using chemical pesticides, and while such techniques such as the treatment of seeds with pesticides have reduced the harmful effects of pesticides on the environment, numerous problems remain that limit the successful application of these methods under actual field conditions.
Application Ser. No. 10/599,307, filed Sep. 26, 2006, describes an improved method for the protection of plants, especially corn plants, from feeding damage by pests. This method reduces the required application rate of conventional chemical pesticides, and also limits the number of separate field operations that are required for crop planting and cultivation.
Mixing of seed samples, as described in application Ser. No. 10/599,307 presents new problems which are sought to be solved by the present application.
In order to ensure adequate application of the mixed seed, individual seeds are to be visually indistinct to a farmer. However, in order to maintain quality control, it is necessary for the seed producer to be able to adequately sample the mixed seed to determine whether the proper ratio is being maintained. Additionally, if seed is returned to the producer without being sold or grown, it is necessary for the seed producer to separate the differing seed types.
This situation is further complicated by regulations, such as the Federal Seed Act as enforced by the Seed Branch of the USDA, which require seed bags to individually identify each seed type present in a bag, as a percentage of the whole, and its germination rate. Unless seeds are in some manner distinguishable from one another, it is impossible to accurately report germination rates and reuse seed. Further, if one seed type has a shorter shelf-life than another, it may be preferable to replace the shorter lived seed while recycling the longer-lived seed. In order to accomplish this, the mixed seed must be easily separable.
Therefore, it is a principle objective of this invention is to provide a method for sorting seeds from one another while maintaining visual indistinctiveness between any two seed types.
It is a further objective of this invention to provide a method of treating one or more fractions of a seed population with an additive to render visually indistinct seed fractions distinctive under specific conditions.
It is a further objective of this invention to provide a method for identifying and quantifying the percentage of differing seed types in a seed sample.